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jtwrace

Uptone Audio Regen

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jtwrace   

From UpTone:

 

Well Jason at Schiit does not like to make claims (I admire that among many other excellent business practices of theirs), but in his long blog/book on HeadFi he does talk about the SQ differences the Wyrd can make. Yet as John pointed out, the degree depends upon both the computer and the DAC. But the design of both the Wyrd and our REGEN is absolutely not just about providing cleaner 5V USBVbus power. One does not need a hub chip, clocks, etc. to do that. In fact, in designing the piece, John and I discussed whether to even interrupt the USB VBus power to provide our own, but of course it made sense to do so.

 

So yes, both the Wyrd and the REGEN will perform their primary purpose even if the DAC does not use 5V Vbus power at all. (John did some trick things to make ours work/sound extra good: 4 layer board with impedance-controlled output, ultra low-noise regulators, external DC supply--Wyrd brings low voltage AC into it, no USB output cable--I'll be providing a USB A>B solid adapter so the tiny box can attach to the DAC and not introduce another USB cable.)

 

As for the advantages, it comes back to the research he has been doing on packet noise (where poor signal integrity makes the DAC's USB PHY and processor work harder--causing internal modulation at both 8KHz packet rate and wideband), power distribution networks, etc. So the REGEN places creation of new and clean USB signal right at the DAC. Kind of like an external version of an audiophile USB card (SOtM, Paul Pang, etc.), but at the correct end of the cable and not powered by the computer. A boon for Mac users for whom such cards don't even exist.

 

I'd like to refer you to some of John's directly related recent writing: http://www.computeraudiophile.com/f10-music-servers/mac-mini-version-computer-audiophile-pocket-server-music-server-step-step-17666/index10.html#post370186

 

Would like to be in production within the next 12 weeks or so. No price set as I have not gotten quotes for milling of the tiny (55mm x 45mm) enclosure's end caps or the PCB fab/stuffing. Here is a pic of the not final version of the board (final is rearranged and has a big capacitor on it).

 

[ATTACH=CONFIG]16047[/ATTACH]

 

P.S. I just realized that this thread is titled "Ethernet to DAC Connection," so this USB hub talk is completely OT. Sorry.

Ethernet to DAC is a bigger project we have also been working on for a long time, but I really need to be careful not to use the forum for promotion. The above already treads that line a bit. Besides, you can find my fairly detailed hinting about out USB>Ethernet Audio Bridge project elsewhere. It is no longer a secret.

Edited by Superdad

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jtwrace   

This was one of John's postings which is quite interesting.

 

Due to the large number of questions I'm not going to quote each one here, I hope I cover them all.

 

The isolation between computer and DAC was not a primary focus of what I am talking about now. Test I did seem to show this is not as big an issue as many previously supposed.

 

This post is primarily about the impact of the PDN on the generation of PS noise at sensitive chips in a DAC (main oscillator, DAC chip). In particular how a packetized data delivery (USB, Ethernet) significantly exacerbates this. Primarily because the packetized system produces current through the PDN with a much greater bandwidth than non-packetized systems (say I2S). Producing PDN to work well over this wide bandwidth is MUCH harder than for a non-packetized system.

 

On the question of WiFi: it is also a packetized system, and because of all the processing going on in WiFi, probably much worse than straight wired Ethernet.

 

On isolation, I have been including full isolation between digital sections and mixed signal sections for many many years. I do not use optical isolators, I do not like them at all, I prefer the GMR (Giant Magneto Resistive) isolators made by NVE. I think they work way better than opto isolators.

 

The important question here is how come an isolator doesn't completely fix things, it seems at first glance that having completely isolated power networks for the digital side and the mixed signal side (I'm calling it mixed signal because there are digital signals (I2S data, clocks) AND analog signals (output from the DAC chips) in the same power domain) should prevent PS noise from going between them. If the power domains were truly isolated they would, BUT the domains are NOT completely isolated, the data is going between them! This is the part that is usually forgotten in these types of discussions.

 

I hope I can convey what is happening here, let's follow a pulse through an isolator between domains and see what happens. Let's assume a real "dirty" digital side, a lot of ground plane noise and power supply noise, and noise riding on top of the digital signal. Lets look at the isolator, it has power and ground connections on the "dirty" side that run the driver that produces the whatever crosses the "barrier" (light, magnetic field, radio waves, whatever). The noise also modulates the "threshold" looking at the input signal. These and the noise and jitter in the signal all add up to a pretty large amount of variation in the field crossing the barrier.

 

On the other side of the barrier you have a much cleaner supply driving the receiver circuit, but the noisy field is going to cause a current in the receiver. Thus noise on the dirty side is going to cause current noise on the clean side as well. The isolator designers try and make them so the physical properties of the receivers have some form of thresholding so this transmitted noise is decreased, but a fair amount still gets through, and it is greater at the low frequency side. But that is not all, the data, the signal you WANT to cross the barrier, also causes current to flow through the PS pins of the clean side of the isolator, and that signal has a lot of jitter on it by now.

 

When the packet noise on the dirty side of the barrier is low, the current noise of the isolator will be lower, when the packet noise is high, the current noise of the isolator will be high. So even though the power supplies are completely separate, packet noise on the dirty side can still make it through an isolator and show up as current noise on the "clean side". If the PDN is very low impedance over a very wide bandwidth this current noise will produce very little voltage noise. If the PDN is not so great, there will be some significant voltage noise. It usually will be reduced from what it was on the dirty side, but still definitely there.

 

Yes putting a whole tracks worth of data in ram, shutting down the packet interface, and grabbing the data out of ram at the audio sample rate should help this, but this is frequently done by a processor and it's memory, that processor is usually producing it's own set of current noise which can cross the barrier. To be really effective it would take a system where the source (whatever it is) fills up the buffer then completely shuts down, nothing drawing power AT ALL from then on, the only thing drawing power is the counter walking through the ram and the ram itself. You definitely would want a simple ram structure, not something like a DDR3 DIMM which has all kinds of stuff going on all the time. The data from the RAM goes over the isolator and on to the DAC chip. This would probably be a very effective isolation scheme, but I don't think anybody has actually ever implemented this.

 

I have been doing some more experiments on this in the last week and have some results to share. I was working with the USB regen Alex mentioned, with the first version I was able to clearly see the packet noise on a scope. I made a new version with an improved PDN, this seemed to work, I could not see any packet noise any more, noise was still there but I could not discern any modulation due to the packet frequency. It sounded significantly better. Later I did some crude PDN analysis and discovered there was a raising in the impedance over a certain frequency range. I figured out I could fix this by adding a single capacitor in the right place. I soldered in that cap and started listening and was startled in the magnitude of the improvement in SQ. The noise looked identical with and without the capacitor, the sound significantly improved.

 

So I think I am on the right track, but it looks like I have already gone beyond what the simple measurements I was doing could detect. Next is to do these tests with the spectrum analyzer, it will probably be able to detect the packet noise buried in the over all noise floor.

 

I hope that answers some of the questions.

 

John S.

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Superdad   

Wow guys, thanks for your enthusiasm! Gives me motivation to move the project along quickly. And I know this early interest will please John too.

John has done his part (I think I mentioned that I just got back from him a final prototype with big cap to improve PDN, and he has already rearranged the board layout), so I could start PCB production any time.

I'll get going on quotes for the milling and printing of the required openings for the end caps, and will start to add up costs so a price can be set.

 

I promise to keep you all updated.

Have a great holiday!

--Alex C.

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jtwrace   
Wow guys, thanks for your enthusiasm! Gives me motivation to move the project along quickly. And I know this early interest will please John too.

John has done his part (I think I mentioned that I just got back from him a final prototype with big cap to improve PDN, and he has already rearranged the board layout), so I could start PCB production any time.

I'll get going on quotes for the milling and printing of the required openings for the end caps, and will start to add up costs so a price can be set.

 

I promise to keep you all updated.

Have a great holiday!

--Alex C.

Yes, get the BOM going so we can get some numbers. ;-) I'm really excited about this and just hope it's reasonably priced.

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Superdad   

Alright gents, better tone it down before I get into trouble with the management. ;)

 

We are not much into crowd-funding/design (unless you want to design a camel), but I'll take input on color combo for the little case. Here are the choices. No promises about going along with the crowd, and in the end there will be only one color combo offered.

 

Remember, this thing will measure just 55mm x 45mm x 18mm

 

Color choices.jpg

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wisnon   
Wow guys, thanks for your enthusiasm! Gives me motivation to move the project along quickly. And I know this early interest will please John too.

John has done his part (I think I mentioned that I just got back from him a final prototype with big cap to improve PDN, and he has already rearranged the board layout), so I could start PCB production any time.

I'll get going on quotes for the milling and printing of the required openings for the end caps, and will start to add up costs so a price can be set.

 

I promise to keep you all updated.

Have a great holiday!

--Alex C.

Fascinating.

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